As a method of analyzing internal structure and defects in a semiconductor device or the like, there is known a cross-section processing and observation method in which a focused ion beam is used for cross-section processing and slicing of a sample to expose a cross-section including a desired structure or a defect, and a scanning electron microscope is used to observe the cross-section. According to this method, an observation target inside the sample can be exposed with pinpoint accuracy, and hence the structure or the defect can be observed quickly.
There is disclosed a method of repeatedly performing cross-section processing and cross-section observation and combining a plurality of acquired cross-sectional observation images to construct a three-dimensional image of a region subjected to the cross-section processing (see JP-A-2008-270073). According to this method, a three-dimensional image of an observation target can be constructed.
Recently, along with densification and reduction in size of semiconductor devices, a device pattern has become finer, and hence, cross-section processing and observation for a minute observation target have been required. In this case, by setting a gap between one cross-section and another cross-section formed by subjecting the one cross-section to slice processing to be extremely small, that is, by reducing a slice width of a focused ion beam, a minute observation target can be exposed in the cross-section and observed.
However, if the slice width is extremely small, it is difficult to measure the width, and hence there has been a problem in reliability of acquired data. For example, it cannot be confirmed whether or not an observation image acquired by a cross-section processing and observation with a slice width of 1 nm is an observation image photographed with an actual slice width of 1 nm. Thus, there has been a problem in that it is difficult to measure an actual shape from the observation image.